This invention relates generally to chronometers and specifically to electronically-operated chronometers with electronic display.
Electronic time keeping circuitry lends itself naturally to the high accuracy requirements of chronometers for navigational purposes. However, despite the proliferation of electronic timepieces available, no apparatus is available to fill the specific need of the navigator. For celestial navigation, the navigator is required to note with particular accuracy the time at which he takes a reading on the position of heavenly bodies. This marking of the time is conventionally done by quickly looking from the sextant to the chronometer and estimating the time required to make the shift or by audibly indicating to a second person, who is already looking at the chronometer, the exact instant of the sextant reading. Another technique used, which is also common in automobile rallys, is to start a stop watch in synchronism with the chronometer and then to stop the stop watch at the moment of interest and to later calculate the exact time of the moment of interest. These methods of noting the time of an event are both cumbersome and subject to error.
The use of present electronic chronometers adds no benefit for the navigator since his potential error in reading the chronometer is much greater than the inherent error of the chronometer. The typical electronic chronometer or timepiece takes the form of a stable source of high frequency oscillations. While some such timepieces use as a signal source the 60Hz waveform present as domestic power, this source is not very stable, is subject to interruption, and is unavailable where many timing functions are required. In portable versions, not operated by a main electricity supply, but rather from batteries, the source of the signal is usually a quartz crystal or timing fork maintained in a state of constant oscillation. The frequency of the signal is then divided or reduced by electronic counters to produce a stable low frequency signal suitable for read-out of the chronometer.
At the present time, the majority of battery-operated chronometers do not utilize electronic digial read-outs, such as light emitting diodes, due to an unacceptably low battery life. A timepiece used as a navigational chronometer, to diplay mean time, must have a battery life of at least several months. In order to achieve this, most crystal controlled battery operated chronometers do not use a digital display but instead, use a conventional analog-type, using hands to show hours, minutes, and seconds. This type of device, although extremely accurate as a timepiece, yields little actual improvement in accuracy since the human error involved in reading still remains.
It is, therefore, the object of the present invention to enable a user to mark the time of the event while observing the event, with no need to observe the timepiece at that instant.
It is also the object of the invention to provide a portable electronic chronometer with suitably low battery drain to permit long battery life which also has digital display to prevent human error in reading the time.
It is a further object of the invention to provide a portable electronic chronometer in which the display of time may be arrested at a particular instant while the time keeping continues to function with no loss in accuracy.
Still another object of the invention is to provide a portable electronic chronometer in which the display of mean time may be restored at will.